Lipogenesis in vivo in lean and genetically obese (ob/ob) mice fed on diets with a high fat content.

The effect of variations in the fat content of the diet on fatty acid synthesis in vivo was determined in lean and genetically obese mice, using the 3H2O incorporation technique. In both lean and obese mice the rate of fatty acid synthesis was higher between 21.00 - 22.00 h than between 09.00 - 10.00 h. When lean mice were given a high fat (low-carbohydrate) diet the rate of lipogenesis in adipose tissue and rest of carcass (whole mouse minus liver and adipose tissue) was less than in similar mice given a high-carbohydrate (low-fat) diet. In obese mice, the rate of lipogenesis in adipose tissue and rest of carcass was unaffected, but liver fatty acid synthesis was reduced. In lean mice fed on diets containing a constant percentage of carbohydrate and protein, increasing the fat content of the diet (and decreasing the proportion of cellulose) produced a decrease in fatty acid synthesis in liver, adipose tissue and rest of carcass, when the measurements were made during the night-time feeding period. During the day-time, the effect of increasing the fat content of the diet was less marked. In obese mice, dietary fat did not supress either the day-time or the post-prandial night-time rate of fatty acid synthesis. It is suggested that the hyperinsulinaemia in obese mice may be able to overcome the inhibitory effect of dietary fat on fatty acid syntheses.